Known power generators comprise:                a converter able to convert a variation of a magnetic field into a difference of potentials between two electric terminals, this converter comprising to that effect:                    an electromechnical transducer able to transform directly a mechanical deformation exerted on this electromechanical transducer into a difference of potentials between the two electric terminals, and            a magnetostrictive layer extending essentially parallel to a reference plane and fixed without any degree of freedom to the electromechnical transducer, this magnetostrictive layer comprising at least one block of magnetostrictive material able to convert a variation of the magnetic field into a mechanical deformation exerted on the electromechnical transducer,                        a magnetic field source including a group of several permanent magnets aligned along an alignment axis, at least one of the group and the converter being movable, alternately, between:                    a first position in which the field lines of the group of permanent magnets provoke a first deformation of the block of magnetostrictive material, and            a second position in which the block of magnetostrictive material has a second deformation different from the first deformation.                        
Such generators are described for example in the application US2004126620A1 or in the article A1 below:                T. Lafont, J. Delamare, G. A. Lebedev, D. I. Zakharov, B. Viala, O. Cugat, L. Gimeno, N. Galopin, L. Garbuio and O. Geoffroy, “Magnetostrictive-piezoelectric composite structures for energy harvesting”, Journal of micromechanics and microengineering, n°22, 2012.        
In the known generators, a single uniaxial permanent magnet or a group of permanent magnets is arranged opposite each block of magnetostrictive material. When a group of permanent magnets is used, the south pole of one permanent magnet is directly coupled to the north pole of the permanent magnet of the same group that follows immediately afterwards along the alignment axis. In other words, the magnetic moments of the permanent magnets of this group are all aligned and in the same direction. This group of permanent magnets therefore forms in reality a single uniaxial permanent magnet. The horizontal section of the single permanent magnet, that is to say its section in a plane parallel to the reference plane, is substantially equal to the section of the block of magnetostrictive material. The length L of the single permanent magnet in the direction of its horizontal magnetic moment is therefore generally a few centimeters. Now, for this single permanent magnet to induce a substantial magnetic field inside the block made of magnetostrictive material, its aspect ratio must be close to one. This therefore imposes that the thickness e of the large permanent magnet, in its vertical direction, is approximately equal to its length L. The surface area of the vertical section of the single permanent magnet is therefore close to L2. This results in a significant size of the single permanent magnet and hence of the generator.
Prior art is also known from:                Xinazhi Dai et al.: “Energy harvesting from mechanical vibrations using multiple magnetostrictive/piezoelectric composite transducers”, Sensors and actuators A, Elsevier Sequoia S.A, Lausanne CH, vol. 166, N°1, 12/31/2010, pages 94-101;        CN202443031U;        US2011/057629A1;        U.S. Pat. No. 4,645,961A.        